Method of coating glass envelopes



Nov. 24, 1942. MICHAEL 2,303,290

METHOD OF COATING GLASS ENVELOPES Filed June 28, 1941 I I2. 10 n Q 7 I 6 I i 6 Fig.4 H1 I I F ig. 1 George A.Michdel, INVENTOR.

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ATTOEN EY Patented Nov. 24, 1942 LIE'IHOD COATING GLASS ENVELOPES George A. Michael, Boston, Mass, assignor to Sylvnnia Electric Products Inc., a corporation of Massachusetts Application June 28, 1941, Serial No. 400,336

1 Claim.

This invention relates to fluorescent tubing and more particularly to apparatus and methods of coating thereof.

An object of this invention is to provide a method of applying a coating of luminescent material to the walls of elongated glass tubes.

Another object is to provide an apparatus for applying a, coating of luminescent material to the walls of elongated glass tubes.

A further object is to provide means whereby a smooth even coating of luminescent material is uniformly obtained through the entire length of the tube.

Other objects, advantages and features will be apparent from the specification taken in conjunction with the drawing in which:

Figure 1 is a front elevation of the tube coating apparatus.

Figure 2 is a side elevational view of the several plates through which the tubes are held.

Figure 3 is a front elevational view of the several plates.

Figure 4 is a top plan view of the several plates.

In the application of a layer of luminescent material to the inner walls of an elongated tubular glass envelope, such as, for example, the type. of tubing used for making fluorescent tubing signs, the attainment of a smooth uniform coating in which the powder firmly adheres to the glass has proved difllcult. Density variations, streaky and spotted coating are a few of the conditions which mar the appearance of the coated tube. By using the apparatus herein described in the manner herein described, a smooth, even coating, free from streaks and spots can be obtained.

In my co-pending application Serial No.

The coating solution 3 is held in the container 4 which is mounted on the support 5. This support 5 is adjustable with respect to height and 364,100, tiled November 2, 1940, I pointed out the" be located directly behind this panel and thus enable the operator of the apparatus to observe the height of the coating solution in the several tubes as they are being coated and to observe the drying of the several tubes after they have been coated.

may be moved up and down within the pedestal 6. The reduction gear I is mounted on the support 8. This reduction gear 1 is connected to a motor which serves as the means of moving the coating solution container 4 up into coating relation to the several tubes 9. The sprocket wheel III on the shaft, projecting from the gear is meshed with the teeth |2 on the solution container support 5.

A mercury switch I3 is pivotally mounted at the top of the rod M. This rod I4 is held in the bracket IS on the side of the coating chamber This mercury switch controls the movement of the solution container 4.

The tubing 9 to be coated is held in position as shown in Figure 1 through a series of plates. The base plate H5 is held between the angle irons I1 and I8 located on each side of the chamber I. The rubber gripping plate I9 is fixed to the top of the base plate I6 and the cover plate 20, on top of the plate l9, serves to keep the rubber gripping plate securely held in position. When a plurality of tubes 9 are to be placed in position to be coated the guide plate 2|, resting on the angle irons 22, is moved up in proximity to the base plate IE to a point where it touches the stops 23. Thisguide plate 2| is held in this position by the clamps 28 as more clearly shown in Figures 2 and 3. With theguide plate held up in this position, it is fairly easy for the operator to insert the tubes 9 in position. The guide plate 2|, the base plate It, the rubber gripping plate l9 and the cover platev 20 all have a plurality of holes therein through which the tubes 0 may be projected. The glass bell 24 is usually moved up from its position shown in Figure 1 when the tubes 9 are being put into coating position in order to permit a metal plate to be inserted between the angle irons 25.and It. This plate enables the operator to position all of the tubes 8 in the same position with respect to height so that later each tube may be completely coated to the very top.

I It should be noted that the diameter of the holes in the metal plates 2|, 20 and I6 is greater than the diameter of the holes in the rubber gripping plate Is. It is desirable to have this condition exist for then the tubing is suspended entirely from the rubber plate. The metal plates do not grip the tubes at any point. scratching or marring the surface of the glass is obviated.

Thus

When all the tubes have been positioned the plate inserted between the angle irons II and 25 to insure uniformity of height of the tubes is removed. The glass bell 24 is dropped down over the tubing in such a manner that the rim thereof rests on the rubber gripping plate II and encircles the cover plate 20. This glass bell 24 is connected to a suction pump line 21 and an air pressure line 28 through the connecting line 23. The motor for moving the coating solution container support 6 may be started and the coating solution container 4 will move up so that the lower ends of the tubes 3 become immersed in the coating solution 3. The

, float 30 has the arm 3| extending upward therefrom through the guide 32.

The valve 33 on the suction line 21 is opened and the coating solution 3 in the container 4 is drawn up into the tubes- 3. This will cause a decrease in the quantity of coating solution in the container 4 and thus the container support 5 will continue to rise so as to insure the immersion of the ends of the tubes 3 in the solution 3. The operator observes the rising coating solution and when it has reached the tops of 'the tubes, the operator opens the valve 34 on the air line 28 and shuts off the suction line through valve 33. This stream of air entering the chamber formed by the glass bell 24 may be caused to pass through a screen 35 to insure an even difiusion of air over the tops of all the tubes 3..

cause otherwise the coating on the tops of the tubes may become very thin before it starts to dry. By allowing a -30 second interval to elapse between the first flushing and the second, a sufficient portion of the top of the tube will have dried enough to reinforce the second coat.

In order to insure a uniform and proper density of the coating as well as one free from streaks and other disfiguring effects, I have found that about three and one-half pounds of air pressure through acne-half inch conduit is desirable.

The returning solution will cause the level thereof in the container 4 to rise. A rising level will cause the arm 3| extending upward from the float 30 to throw the mercury switch i3 and thus reverse the motor, so that the solution container support 5 will move downwardly. When begun, the top of the tube is dried very rapidly.

This is especially desirable on the first coat be- This gives a. smooth even coating. The total drying time is about eleven minutes. Any substantial decrease in this drying time will prove deleterious. For example, if the drying time were speeded up, streaky coating would result and there would be a lack of density uniformity. Although l. have used three and one-half pounds of pressure through a one-half inch conduit, it must be understood that these measurements may be varied so long as the rate of flow remains substantially the same.

Figure 2 is a side and Figure 3 a front view of the several plates described above when they are in the locked position during the loading and unloading operations.

Figure 4 is a top plan view of the cover plate 20, the rubber-gripping plate l3 and the base plate i3.

What I claim is:

The method of coating elongated glass envelopes with a suspension of luminescent material, said method comprising: drawing up the suspension into the glass envelopes by suction; allowing the suspension to drain'therefrom; passing a stream of air through the glass envelopes from the top thereof until the tops of said glass envelopes start to dry; drawing up the suspension into the glass envelopes by suction a second time; allowing the suspension to drain therefrom; and passing a, stream of air through the glass envelopes from the top thereof until the 

